(a) Each operator shall continuously maintain the average
concentration of respirable dust in the mine atmosphere during each shift to
which each miner in the active workings of each mine is exposed at or below
2.0 milligrams of respirable dust per cubic meter of air as measured with an
approved sampling device and in terms of an equivalent concentration
determined in accordance with §70.206 (Approved
sampling devices; equivalent concentrations).
(b) Each operator shall continuously maintain the average
concentration of respirable dust within 200 feet outby the working faces of
each section in the intake airways at or below 1.0 milligrams of respirable
dust per cubic meter of air as measured with an approved sampling device and
in terms of an equivalent concentration determined in accordance with
§70.206 (Approved sampling devices; equivalent
concentrations).
